Mining continues to be one of the most dangerous industries in America, as evidenced by the recent collapse in the Crandall Canyon Mine in Utah, and the Sago Mine in West Virginia. When a mine collapses it can leave survivors stranded over 1000 feet below the surface with all means of communications cutoff. Landlines, which serve as the primary means of communication, are instantly severed by the force of the collapse, and radio signals are not able to penetrate the earth; therefore, the survivors are unable to communicate with the surface. The highest priority after a mine collapse is to drill into an area near where the survivors are located, create an air shaft and pump in oxygen. The severing of the land lines by the collapse, however, makes it difficult, if not impossible to identify the location of the survivors. Because every hour counts, rescue crews need a reliable and precise means of locating and communicating with survivors.
The currently available communication systems for use in mines comprise of a mix of wired, radio, wireless and Through the Earth communication systems. Wired transmissions depend on signals sent along wires and cables. As mentioned, wires and cables are susceptible to being snapped or damaged in a mine collapse. Radio signals require open air for signal propagation; therefore, mine collapses block the radio signals. Wireless systems often employ a special antenna cable called a “leaky feeder” to form a back bone for the wireless transceivers, allowing the signal to hop for short distances along available conductors, such as electrical wires and water lines. Since wireless systems still require wire-bound components, they can fail during mine collapses when cables are broken. Through the Earth wireless systems send magnetic waves through the ground, but require extensive above the ground loop antennas in order to communicate with miners below. The loop antennas required can be hundreds of feet in size, if not larger. In addition, most Through the Earth systems communicate only one-way, surface to underground. In order to enable two-way communication, including underground to surface communication, the same extensive loop antennas would have to be located underground.
Information relevant to attempts to address these communication problems can be found in U.S. Pat. No. 7,307,915 (issued Dec. 11, 2007), U.S. Pat. No. 7,149,472 (issued Dec. 12, 2006), U.S. Pat. No. 6,928,030 (issued Aug. 9, 2005), U.S. Pat. No. 6,584,406 (issued Jun. 24, 2003), U.S. Pat. No. 4,066,992 (issued Jan. 3, 1978); U.S. patent application Ser. No. 2008/0021658 (published Jan. 24, 2008), U.S. patent application Ser. No. 2007/0250269 (published Oct. 25, 2007); PCT Publication Nos. WO/2007/143744 (published Dec. 13, 2007), WO/2006/067432 (published Jun. 29, 2006), WO/2005/002066 (published Jan. 6, 2005), WO/2004/068169 (published Aug. 12, 2004). However, each of these references suffers from one or more of the following disadvantages: 1) transmits a short duration signal, or a frequency modulated signal that can be missed in the enormous background noise of the earth; 2) transmits a broad range frequency signal that can be masked by the background noise of the earth; 3) transmits signals only from the surface to underground; 4) uses very large seismic wave transmitters; and 5) requires extensive infrastructure both above and below the ground.
Relevant facts: 1) George W. Flathers III, joint inventor, presented the paper titled “Emergency Underground Communication Using Seismic Waves” at the National Conference on Undergraduate Research 2007, on Apr. 14, 2007 at Dominican University of California in San Rafael, Calif.; 2) Discovery Channel Canada featured the disclosure on May 23, 2007 and a copy of the feature is posted at http://academics.vmi.edu/ee_js/Research/ELFSD/ELFSD.htm at the Discovery Channel link; 3) WSLS TV Channel 10 out of Roanoke, Va. featured the disclosure no earlier than May 15, 2007 and a copy of the feature is posted at http://academics.vmi.edu/ee_js/Research/ELFSD/ELFSD.htm at the WSLS link.
For the foregoing reasons, there is a need for an improved communication system for survivors of a mine collapse to contact the rescue teams above ground.